Characterization of three-fraction mycobacillin synthetase

Molecular biology of antibiotic production in Bacillus

Several species of the genus Bacillus produce peptide antibiotics which are synthesized either through a ribosomal or non-ribosomal mechanism. The antibiotics gramicidin, tyrocidine, and bacitracin are synthesized nonribosomally by the multienzyme thiotemplate mechanism. Surfactin and mycobacillin are also synthesized nonribosomally but by a mechanism that, apparently, is distinct from that of the multienzyme thiotemplate. Other antibiotics such as subtilin are gene encoded and are ribosomally synthesized. Molecular genetic and DNA sequence analysis have shown that biosynthesis genes for some antibiotics are clustered into polycistronic transcription units and are under the control of global regulatory systems that govern the expression of genes that are induced when Bacillus cells enter stationary phase of growth. Future experiments involving the molecular dissection of peptide antibiotic biosynthesis genes in Bacillus will be attempted in hopes of further examining the mechanism and regulation of antibiotic production.

Role of ATP and enzyme-bound nascent peptides in the control of elongation for mycobacillin synthesis

The enzyme fraction A, a constituent of the three-fraction (A, B and C) enzyme complex mycobacillin synthetase, elongated tri- and tetra-peptides, under enzyme-bound conditions, to tetra- and penta-peptides respectively in the presence of the 'next' amino acid (in the mycobacillin sequence). The enzyme fraction B synthesized hexapeptide from free pentapeptide and the next amino acid, but synthesized heptapeptide from hexapeptide only under enzyme-bound conditions in the presence of the next amino acid. Similarly, the enzyme fraction C synthesized decapeptide from free nonapeptide in the presence of the next amino acid, but undecapeptide only from enzyme-bound decapeptide in the presence of the next amino acid during the elongation process. The Km values for the initiating reactions for each of the three enzyme fractions were 6-7-fold lower than those for the succeeding reactions catalysed by each of the enzyme fractions. The specificity of the initiation and elongation is discussed in the light of these findings.